Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

traylor:Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

traylor:Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

I was about to agree with you but I looked at it again and I'm pretty sure it is Io's shadow. Even though Jupiter seems pretty straight on, it could be 5-10 degrees off or so off and the crescent would hardly be noticable, yet that should be enough to account for the offset of the shadow. OTOH I don't see Io at all in the first half (not that I expect to: it would be a speck in front of and underexposed against Jupiter, but I didn't even see a hint of it).

John Nash:traylor: Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

And just how have you determined these angles?

By looking at a frame like this:

Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

traylor:You can see the shadow of Europa Io on Jupiter's cloud tops, too.

I don't think so.

Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

The only way Jupiter could appear as a crescent is if it were orbiting between us and the sun. As it is, even at the maximum possible phase angle, Jupiter will show only a very slight shadow along one limb. In this video, the sun is somewhere behind the viewer, a bit off to one side of an Earth-Jupiter line.

Additionally, the orbits of Jupiter and its moons are known with enough accuracy that shadow transits can be predicted as accurately as eclipses are here on Earth. If there's a dark spot on Jupiter in position X at time Y, a quick check of an ephemeris will either confirm or rule out its being a moon's shadow.

traylor:Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

Are you aware that Io's orbital radius is about 6 Jupiter radii?

By my Q&D reckoning, the Sun's about 6 degrees off. Basically, Io is about half a Jupiter radius from the shadow. Io is about 5 Jupiter radii from Jupiter's surface. Therefore, the angle the sun makes with respect to the direction of this photograph is about arctan(0.5/5) = arctan(0.1) = 5.7 degrees. A 5.7 degree angle would not produce much of a crescent.

traylor:John Nash: traylor: Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

And just how have you determined these angles?

By looking at a frame like this:

[i6.photobucket.com image 416x286]

Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

traylor:John Nash: traylor: Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

And just how have you determined these angles?

By looking at a frame like this:

[i6.photobucket.com image 416x286]

Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

In this frame, the sun would be somewhere above and behind the viewer's left shoulder.

Mister Peejay:traylor: John Nash: traylor: Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

And just how have you determined these angles?

By looking at a frame like this:

[i6.photobucket.com image 416x286]

Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

I know a good telephoto will cause some distortion, but doesn't Jupiter look like a tiny dot when standing on the moon.

Why does it look rather large compared to the in focus lunar landscape? Shouldn't the moon be much, much more zoomed in?

Well, those aren't the same things. The moon is relatively close to the Earth, and Jupiter is quite far from both the Earth and the Moon. If you put in a lens that magnifies vision by 200x and look at the Moon with Jupiter in the background, you'll be able to see surface details of the moon. However, that's not the same as standing on the moon. If you were standing on the moon looking at Jupiter with the naked eye, it would indeed just be a bright dot. However, if you're viewing from Earth with 200x magnification, you're still looking at Jupiter with 200x magnification regardless of the position of the moon.

The proportions do seem about right. My telescope is nothing fancy, but at 1325 focal length and a 25mm eyepiece, Jupiter fills about 1/8th to 1/10th of the field of view. The moon fills nearly all the field of view. Probably 9/10 of it at least. At this magnification (55x) Jupiter is distinct and you can make out the bandings. The moons are still just bright dots though. If the Moon and Jupiter were in the same field of view I suspect that I would get similar results.

traylor:John Nash: traylor: Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

And just how have you determined these angles?

By looking at a frame like this:

Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

You are assuming that tiny dot above and to the left of the shadow is the moon casting the shadow. Maybe the shadow is being cast by a moon you can't easily see. Juniper has, like, 87.5 moons.

The article claimed that it was Io. I believe he was suggesting the same point you are. It was either a shadow caused by a different (unseen) moon rather than Io (the one visible in the photo), or it's actually some kind of atmospheric condition that looks like a shadow.

I know a good telephoto will cause some distortion, but doesn't Jupiter look like a tiny dot when standing on the moon.

Why does it look rather large compared to the in focus lunar landscape? Shouldn't the moon be much, much more zoomed in?

Well, those aren't the same things. The moon is relatively close to the Earth, and Jupiter is quite far from both the Earth and the Moon. If you put in a lens that magnifies vision by 200x and look at the Moon with Jupiter in the background, you'll be able to see surface details of the moon. However, that's not the same as standing on the moon. If you were standing on the moon looking at Jupiter with the naked eye, it would indeed just be a bright dot. However, if you're viewing from Earth with 200x magnification, you're still looking at Jupiter with 200x magnification regardless of the position of the moon.

The proportions do seem about right. My telescope is nothing fancy, but at 1325 focal length and a 25mm eyepiece, Jupiter fills about 1/8th to 1/10th of the field of view. The moon fills nearly all the field of view. Probably 9/10 of it at least. At this magnification (55x) Jupiter is distinct and you can make out the bandings. The moons are still just bright dots though. If the Moon and Jupiter were in the same field of view I suspect that I would get similar results.

Works for me. Just seemed fishy being able to see the curvature of the moon.

I'd would have thought it be much more flat if we were viewing Jupiter with such clarity an magnification.

I know a good telephoto will cause some distortion, but doesn't Jupiter look like a tiny dot when standing on the moon.

Why does it look rather large compared to the in focus lunar landscape? Shouldn't the moon be much, much more zoomed in?

It's not distortion, it's a compression of distance between objects. Either way, I was at our star party last week, with 'scopes focused on both the moon and Jupiter, and while none had Jupiter sized quite that well, the moon was a little smaller than it is in that video. I think it works just fine this way, and I would be extremely surprised if Bad Astronomy farked something like this up.

traylor:John Nash: traylor: Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

And just how have you determined these angles?

By looking at a frame like this:

[i6.photobucket.com image 416x286]

Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

Keep in mind that while Io looks to US like it's up and to the left, with these types of distances, it could totally be at the angle to leave a shadow exactly there, also considering that the Sun is not necessarily directly behind us when this is all happening. It's all about perceived vs. actual angles of viewing.

Mikey1969:traylor: John Nash: traylor: Looks like Jupiter is fully lit from our point of view. In order to Io to cast a shadow on Jupiter the Sun needs to be somewhere far to the top and to the left, and that would make Jupiter look more crescent-y. And, a similar spot is seen when Jupiter goes behind the Moon a bit more than an hour earlier. IMHO it's either an other moon or a spot in the clouds.

And just how have you determined these angles?

By looking at a frame like this:

[i6.photobucket.com image 416x286]

Tell me you what you think, I'm curious. Where can the Sun be in order to cast the shadow of Io on the Jupiter and at the same light up the planet as we see?

Keep in mind that while Io looks to US like it's up and to the left, with these types of distances, it could totally be at the angle to leave a shadow exactly there, also considering that the Sun is not necessarily directly behind us when this is all happening. It's all about perceived vs. actual angles of viewing.

I forgot to come back to this thread, but exactly that. Io is just a dot there. You have no idea how far in front of Jupiter it is. Any perceived relative position is a trick of the eye.

Mikey1969:Keep in mind that while Io looks to US like it's up and to the left, with these types of distances, it could totally be at the angle to leave a shadow exactly there, also considering that the Sun is not necessarily directly behind us when this is all happening. It's all about perceived vs. actual angles of viewing.

We know the Sun is nearly directly behind us. When you're on Earth, photographing a nearly full Moon, that's where the Sun is. However, even if the Sun is only a few degrees aside it's still enough to cause that shadow.

John Nash:I forgot to come back to this thread, but exactly that. Io is just a dot there. You have no idea how far in front of Jupiter it is. Any perceived relative position is a trick of the eye.

We know quite well how far in front of Jupiter Io is in this picture: 340,000 km. (That is, 410,000 km orbital radius - 70,000 km Jupiter radius.) But I think your point is that the distance Io is probably a lot different that we'd imagine it is just by looking at the photograph, and that's why it might seem like Io couldn't produce the shadow.

I know a good telephoto will cause some distortion, but doesn't Jupiter look like a tiny dot when standing on the moon.

Why does it look rather large compared to the in focus lunar landscape? Shouldn't the moon be much, much more zoomed in?

50-year amateur astronomer, here. Jupiter subtends about 45 arc seconds (0.75 arc minute) while the moon subtends about 30 arc minutes. (These apparent sizes vary by about 5% or so but the general point is valid) So Jupiter appears about 30/0.75 = 40 times smaller than the moon. The video shows the occultation exactly as I have seen them through a telescope at about 150 to 200 power.

To the other Farker who thought that there was a shadow transit in progress at the time of Jupiter's egress - you win first prize! The shadow of Io was on Jupiter as Jupiter emerged from behind the moon. (Citation: Handbook of the Royal Astronomical Society of Canada as well as Sky Safari Pro and Starry night Pro planetarium programs. I spent 30 minutes researching this post to get it right)

Watch Jupiter's egress again and you will see the tiny black dot of the shadow...